As a general rule, acid type fuel cell power systems will operate more efficiently and with increased power density (lower cost) in a pressurized environment. Elevated steam pressures are generated in the fuel cell stacks of the system by heating water to elevated temperatures in the cooling system. The steam pressure will thus be proportional to the cell stack temperature. In an acid fuel cell system, the elevated pressure on the cathode or oxygen side of the system will be created by comoressing air fed into the system by means of a turbocompressor which is operated with waste heat from the power plant. On the fuel side, raw hydrocarbon fuel will be elevated in pressure by an electrically driven pump or compressor and fed into a catalytic reformer vessel where the fuel is mixed with the heated steam at an elevated pressure. The raw fuel is thus catalytically converted to a hydrogen enriched fuel gas suitable for use in the electrochemical reaction in the fuel cells. This enriched fuel is fed to the anode side of the fuel cell power section of the plant from the reformer. This catalytic reforming of the fuel gas and the electrochemical reactions in the fuel cells proceed more vigorously at higher pressures and temperatures. In order to ensure proper fluid flow in the system, the reactant pressures cannot be higher than the steam pressure.
In the prior art, the steam for the reformer has typically been provided by routing steam from the coolant, after the latter has cooled the cells, to the reformer. Such a system is shown in U.S. Pat. Nos. 3,982,962 Bloomfield, granted Sept. 28, 1976. When coolant steam is used in the reformer, the temperature and pressure of the steam in the reformer are limited by the operating temperatures of the cells in the power section which are being cooled by the coolant. In acid fuel cells, and particularly in phosphoric acid fuel cells, the material from which the cell components are made impose a maximum permissible operating temperature on the cells of about 450.degree. F. If the operating temperatures of the cells exceed the maximum permissible operating temperatures, the cells will begin to fail. Acid fuel cell stacks are cooled by coolant passages which are interspersed throughout the stacks and which carry a coolant fluid, typically water. The coolant passages are preferably pipes which traverse the cell stack. These coolant pipes will typically be spaced apart in the stack so that each coolant pipe level will serve to cool about four or so cells on each side (above and below) the coolant pipe levels. A coolant system of this general type is disclosed in U.S. Pat. No. 4,574,112, Breault et al., granted Mar. 4, 1986. With this type of coolant system it will be appreciated that the coolant temperature will not reach the level of the temperature of the cells because the cooling is not performed one-on-one with the cells. For example, if one were to desire to operate the fuel gas reformer at a pressure of 450 psi to feed hydrogen-rich gas to fuel cell stacks operating at about 400 psi, the pressure in the coolant tubes in the power section of the stack would have to be greater than 450 psi. In order to produce this 450 psi coolant pressure, the temperature of the coolant steam would have to be greater than 460.degree. F. in the coolant tubes. To achieve this 460.degree. F. steam temperature in the coolant tubes, the cells would have to operate at temperatures greater than 500.degree. F., which is above the maximum permissible extended operating cell temperature. It is thus apparent with the cooling and steam reforming systems of the prior art, one must not operate the fuel gas reformer at pressures in excess of about 175 psi, and that this pressure limit is the direct result of the maximum permissible power section fuel cell operating temperatures. This also places an upper limit of less than 175 psi on the operating pressure in the cells.